1. Field of the Invention
The present invention relates to the filed of MIMO (Multiple-input Multiple-output) communication technology, and particularly to a signal detection method.
2. Background of the Invention
The spatially multiplexed (SM) MIMO (Multiple-Input Multiple-Output) technique can achieve a relatively high data transfer rate without increasing spectral bandwidth or transmit power, and thus has been greatly developed as a key technique in the fourth generation mobile communication. In a SM MIMO communication system, the data transfer rate can be increased proportionally by increasing the number of transmitting antennas and using a higher order modulation. Increasing the number of transmitting antennas can proportionally increase the number of spatially transmitted data streams, thus proportionally increasing the data transfer rate. A higher order modulation can expand the modulation constellation set, increase the information content carried by each bit, and thus increase the data transfer rate of each single data stream. However, since the signal received by each receiving antenna is always a mix of all the transmitted signals after passing through different channels, increase in the number of the transmitting antennas will increase the interference between the transmitted signals. In a higher order modulation, the larger a modulation constellation is, the smaller the Euclidean distance between symbols is, which indicates a larger interference between the symbols. Therefore, the spatial multiplexed MIMO communication system increases the data transfer rate at the cost of greatly increasing difficulty in signal detection.
The conventional ML (Maximum Likelihood) algorithm is the best signal detection technique in a MIMO system. It is an ergodic searching algorithm which searches the candidate transmitted vector with a minimum Euclidean distance between its channel response and the received signals. However, the complexity of the ML algorithm can be extremely high when the constellation or the number of transmitted antennas is large, which makes it not conducive for an engineering implementation. There are also various signal detection methods with a lower complexity, including linear detection and nonlinear detection algorithm. However, decrease in the computational complexity usually leads to a increase in the bit error rate. Linear detection algorithms, such as the ZF (Zero Forcing) algorithm and the LMMSE (Linear Minimum Mean Square Error) algorithm, have the lowest computational complexity, but the bit error rate is relatively high, which results in that the linear detection algorithms are not qualified in terms of detection accuracy and thus can not be used directly in reality. Nonlinear detection algorithms, such as the V-BLAST (Vertical Bell Laboratories Layered Space Time) algorithm, the PIC (Parallel Interference Cancellation) algorithm and the SD (Sphere Decoding) algorithm, have a lower bit error rate but a higher computational complexity. To find a signal detection method with a good compromise between detection accuracy and computational complexity has become a hot topic in research.